Although metals are a common component of our contemporary environment, there has been little interest in metal mutagenesis. This is unfortunate since many metals are carcinogens and there is accumulating evidence that most mutagens are carcinogens. The purpose of this study is to elucicate the mode(s) of mutagenesis of several metal mutagens by examining the specificity of induced mutations with the trpA system of Escherichia coli where the amino acid changes involved in discrete revertant classes are known. First we will determine spontaneous and metal-induced reversion frequencies for each mutant trpA allele. By distinguishing the revertant classes, with simple chemical tests, of trpA base-pair substitution and frameshift mutants, we will be able to deduce which particular transition, transversion, deletion or insertion event occurred during reversion. With this data the spontaneous and metal-induced reversion frequencies for specific base-pair changes can be calculated. The relative mutagenesis for the particular metal can be derived by comparing the spontaneous reversion frequency for a particular base-pair change with the frequency in the presence of the metal. This will demonstrate the degree of enhancement by a metal for a specific base-pair change. By characterizing the specificity of metal mutagenesis we hope to eludicate the mode(s) of metal mutagenesis and reveal how metals interact with DNA during carcinogenesis.